Document WO 2010/020698 describes equipment used for storing, dispersing and dissolving polymers in powder form, more particularly based on acrylamide. The polymer solution is then metered out and used in hydraulic fracturing operations intended for the production of shale gas or dispersed petroleum.
This equipment has significant operating constraints since fracturing operations assemble numerous vehicles (lorries, trailers), sometimes more than 100, comprising electrical generators, transportation of pumps, mixers, devices for dissolving and adding adjuvants, control rooms and above all large amounts of sands or ceramic beads that are used to keep the fractures open.
The cost of such operations is very high and one of the success factors is the total time for fracturing and for the transfer of the equipment, which ensures the profitability of the fracturing run. It is therefore essential that the equipment used gives the best performances without risk of interruption. If not, the well to be fractured may clog up, which can be catastrophic.
All the equipment must therefore be able to be moved on wheels, either by lorries or on trailers, while taking into consideration the road weight restrictions which depend on the geographical zone in question. Usually, the weight excluding the chassis should not exceed 20 to 24 tonnes and the length 12 to 14 meters. It is furthermore necessary that it be immediately available after its journey without wasting time in the initial filling operations.
The acrylamide-based polymers injected are polymers, preferably of high molecular weight, greater than 10 million, usually greater than 15 million. Their composition depends on the salinity of the water and above all on the amount of divalent metals (Ca++, Mg++).                For fresh water, acrylamide/acrylic acid copolymers (60/40 mol % to 90/10 mol %) are usually used.        For more saline waters, weakly anionic or nonionic copolymers containing from 0 to 10 mol % of acrylic acid or having a low content of sulphonated monomer (ATBS acrylamido tert-butyl sulphonate) are used;        For very saline waters, use may be made of acrylamide/trimethylaminoethyl acrylate chloride copolymers (90/10 mol %) for example.        In extreme cases, use may be made of polymers of DADMAC (diallyldimethyl-ammonium chloride), NVP (N-vinylpyrrolidone), etc.        
Although the equipment described in document WO 2010/020698 performs well, it is however limited in terms of the amount of polymer treated, and has the following constraints:                The polymer is supplied as 25 kg bags, at best as 750 kg big bags, at a speed that is incompatible with large-scale recovery operations.        Impossibility of being supplied in bulk during operation.        Difficulty of metering out and dispersing the polymer at high concentration so as to limit the volumes of polymer dispersion and/or solution in the equipment.        Difficulty in avoiding the formation of aggregates (known as fish eyes), which can only dissolve over a very long time and which, furthermore, may block the pumps.        Difficulty in dissolving the suspension within a short period, since the volumes available on a lorry are limited.        Difficulty in pumping the polymer solution in a controlled manner in the mixer, which comes before the very-high-pressure injection pump and which homogenizes all the ingredients.        
Some people use metal containers that are difficult to handle on ground that is often muddy.
The current development, with the increase in the length of horizontal bore holes, is to tend towards larger fracturing operations. A few months ago, the operations required from 4 to 8 tonnes of polymer per operation and the equipment described in document WO 2010/020698 is suitable for this type of operation.
Nowadays, the amounts injected range from 9 to 15 tonnes and probably in the future about 20 tonnes per operation, and the equipment described in document WO 2010/020698 is no longer suitable.